What's the difference between casting and forging automobile parts?

2020-01-16 16:26:09

Casting is the production method of pouring molten metal into the cavity of the mold, cooling and solidification to obtain products.

In the process of automobile manufacturing, there are many automobile parts made of cast iron, which account for about 10% of the whole vehicle weight, such as cylinder block, transmission case, steering gear case, rear axle case, brake drum, various brackets, etc.

Sand mold is usually used to make iron castings. The raw material of sand mold is mainly sand, which is mixed with binder and water. The sand mold material must have a certain bonding strength, so as to be molded into the required shape and be able to resist the erosion of hot metal without collapse. In order to form a cavity in the sand mold which is consistent with the shape of the casting, the wood mold must be made first. The volume of hot molten iron will be reduced after cooling. Therefore, the size of the wood mold needs to be increased according to the shrinkage based on the original size of the casting, and the surface to be machined should be thickened accordingly.

The hollow casting needs to be made into sand core and corresponding core wood mold (core box). With a wood mold, you can turn over the cavity sand mold (casting is also known as "turning sand"). When making sand mold, we should consider how to separate the upper and lower sand boxes to take out the wood mold, and also consider where the molten iron flows in and how to fill the cavity to get high-quality castings. After the sand mold is made, it can be poured, that is, molten iron is poured into the cavity of the sand mold. When pouring, the temperature of molten iron is 1250-1350 ℃, which is higher when smelting.

Forging is widely used in automobile manufacturing. Forging is divided into free forging and model forging. Free forging is a processing method that the metal blank is put on the anvil to bear the impact or pressure to form. The rough parts of automobile gears and shafts are processed by free forging.

Model forging is a process in which the metal blank is placed in the die bore of the forging die to bear the impact or pressure. Model forging is a bit like the process of dough being pressed into biscuit shape in the mold. Compared with the free forging, the shape of the workpiece made by die forging is more complex and the size is more accurate. Typical examples of automobile die forgings are: engine connecting rod and crankshaft, automobile front axle, steering knuckle, etc.